1. Field of the Invention
The present invention relates generally to a wireless power transmitter and a method for controlling the same, and more particularly, to a wireless power transmitter capable of communicating using a predetermined scheme and a method for controlling the wireless power transmitter.
2. Description of the Related Art
Due to their portability, mobile terminals, such as cellular phones and Personal Digital Assistants (PDAs) are powered by rechargeable batteries. In order to charge a rechargeable battery, a separate charging device is used to supply electrical energy to the battery. Generally, the charging device and the battery have their own external contact terminals, so that the charging device and battery can be electrically connected by physically connecting their contact terminals to each other.
However, when using the above-described contact-type charging method, the contact terminals, which may protrude outward from the charging device and/or battery, are may be contaminated by foreign substances, causing a battery charging failure. A battery charging failure may also occur even when the contact terminals are exposed to moisture.
In order to address these and other problems and disadvantages, wireless and contactless charging technologies have recently been developed and used in many electronic devices.
This wireless charging technology, which uses wireless power transmission/reception, may refer to, for example, a system in which a battery of a cellular phone may be automatically or wirelessly charged when a user merely puts the cellular phone on a charging pad without connecting the cellular phone to a separate charging device via a charging connector. Generally, wireless electric toothbrushes or wireless electric shavers are well known examples of devices employing wireless charging technology. Wireless charging technology can improve the waterproof functions of devices, and can increase the portability of electronic devices since the technology does not require a wired charger. Technologies related wireless charging are expected to significantly evolve along with an upcoming increased usage of electric cars.
Wireless charging technologies can be roughly classified into an electromagnetic induction scheme using coils, a resonance scheme using resonances, and a Radio Frequency (RF)/microwave radiation scheme that transfers electrical energy by converting the electrical energy into microwaves.
From among the above-listed schemes, the electromagnetic induction scheme has been primarily used. However, experiments to wirelessly transfer power from a distance of tens of meters using microwaves have been successful. Therefore, an era of wirelessly charging all electronic products without wires at any time or location may arrive in the near future.
The electromagnetic induction-based power transmission method includes transferring power between a primary coil and a secondary coil. If a magnet moves around a coil, an induced current is generated. Based on this principle, a transmitter generates magnetic fields and a current is induced at a receiver due to the change in the magnetic field, generating electrical energy. This phenomenon is referred to as electromagnetic induction, and a power transmission method based thereon provides excellent energy transmission efficiency.
In 2005, a system in which electricity is wirelessly transferred by using resonance scheme-based power transmission principle as a coupled mode theory, which can be applied even when an electronic device is several meters apart from a charging device was developed. The wireless charging system uses a physics concept, called resonance, where, if a tuning fork sounds, a nearby wine glass also sounds at the same frequency. Resonance signals of electromagnetic waves containing electrical energy instead of ringing a tuning fork were generated. The resonance electrical energy is directly transferred only to the electronic device having a resonant frequency, and the rest of the resonance electrical energy is re-absorbed as electromagnetic fields instead of spreading into the air, and therefore, unlike other electromagnetic waves, the resonance electrical energy does not affect nearby machines and bodies.
Many studies on the wireless charging have been conducted in recent years. However, no standard has been proposed for the wireless charging order, the search for wireless power transmitters/receivers, the selection of a communication frequency between wireless power transmitter and receiver, the wireless power adjustment, the selection of a matching circuit, and the allocation of communication time to each of wireless power receivers in one charging cycle, for example. In particular, there is a need for a standard for a structure and procedure in which a wireless power receiver selects a wireless power transmitter from which it will receive wireless power.
A wireless power transmitter and a wireless power receiver may communicate with each other based on a predetermined scheme, such as, Zig-bee and Bluetooth Low Energy (BLE). The available communication distance increases by means of the out-band scheme such as Zig-bee and BLE. Accordingly, the wireless power transmitter and the wireless power receiver may communicate with each other even when these devices are spaced far apart from each other. For example, the wireless power transmitter may communicate with the wireless power receiver, even if the wireless power transmitter is placed in the relatively long distance where it cannot transfer wireless power.
In the example of FIG. 1, a first wireless power transmitter TX1 and a second wireless power transmitter TX2 are placed. In addition, a first wireless power receiver RX1 is placed on or over the first wireless power transmitter TX1, and a second wireless power receiver RX2 is placed on or over the second wireless power transmitter TX2. The first wireless power transmitter TX1 needs to transfer its power to the first wireless power receiver RX1 placed adjacent thereto. Likewise, the second wireless power transmitter TX2 needs to transfer its power to the second wireless power receiver RX2 placed adjacent thereto. Preferably, therefore, the first wireless power transmitter TX1 communicates with the first wireless power receiver RX1, and the second wireless power transmitter TX2 communicates with the second wireless power receiver RX2. However, as the communication distance increases, the first wireless power receiver RX1 may join the wireless power network controlled by the second wireless power transmitter TX2, while the second wireless power receiver RX2 may join the wireless power network controlled by the first wireless power transmitter TX1. This situation is called “cross connection”. In the present example, the first wireless power transmitter TX1 transfers power required by the second wireless power receiver RX2, instead of the power required by the first wireless power receiver RX1. If the second wireless power receiver RX2 has a higher capacity than the first wireless power receiver RX1, the first wireless power receiver RX1 may be overcharged. However, if the second wireless power receiver RX2 has a lower capacity than the first wireless power receiver RX1, the first wireless power receiver RX1 may be undercharged.